Electrical properties and structure of p-type amorphous oxide semiconductor xZnO•Rh2O3

p-Type conduction in amorphous oxide was firstly found in zinc rhodium oxide (ZnO-Rh2O3) (Adv. Mater 2003,15,1409), and it is still the only p-type amorphous oxide to date. It was reported that an ordered structure at the nanometer scale was contained and its electronic structure is not clear yet. In this paper, optoelectronic and structural properties are reported in detail for xZnO center dot Rh2O3 thin films (x = 0.5-2.0) in relation to the chemical composition x. All the films exhibit positive Seebeck coefficients, confirming p-type conduction. Local network structure strongly depends on the chemical composition. Transmission electron microscopic observations reveal that lattice-like structures made of edge-sharing RhO6 network exist in 2-3 nm sized grains for rhodium-rich films (x = 0.5 and 1.0), while the zinc-rich film (x = 2) is completely amorphous. This result indicates that excess Zn assists to form an amorphous network in the ZnO-Rh2O3 system since Zn ions tend to form corner-sharing networks. The electronic structure of an all-amorphous oxide p-ZnO center dot Rh2O3/n-InGaZnO4 junction is discussed with reference to electrical characteristics and results of photoelectron emission measurements, suggesting that the p/n junction has large band offsets at the conduction and valence bands, respectively.